Advice for new solar+battery install for a newbie

[Jason213]

Hi everyone

 

I’ve been thinking and reading about solar panels for some time, and to be honest I’ve found it a bit of a minefield of information. I haven’t started contacting suppliers/installers yet as I want to know what I want to achieve before getting quotes in, although I have registered with solartogether.co.uk.

 

My family:

2 adults, and 2 young children (1 and 3).

No EV yet.. just two diesel cars and will probably change to one EV in 3-5 years time.

Mrs and kids are home by 4pm 3 days per week and home the rest of the time (apart from me working FT).

 

Current house:

New build house built 2017 (120 sq mtr) in the South East (GU32 post code).

Combi boiler (gas 35 kw) for hot water and heating.

EPC rating B (84) - Air permeability 4.4 m³/h.m² (as tested)

Well insulated with additional loft insulation which I have done.

Air con installed, which can also heat as well as cool.

 

The house roof is 8.5mtrs wide with no shading and faces SSSW as below (this could hold 7x2 rows). We also have a double garage facing the same orientation, which could hold a second array. That is 6.5 mtrs wide – I’m not sure if it could fit 5x2 rows, but definitely could fit 5 panels.

 

Current Energy Usage

Elec usage daily:

Average 8.46 kwh per day,

(max 18 kwh)

(5% of the time 12 kwh or more since we’ve lived here)

(5% of the time 4.5 kwh or less)

 

Gas usage daily:

Average 20.6 kwh per day (average over the year)

(38 kwh in all the December’s)

(Max 67 kwh)

(5% of the time 45 kwh or more)

 

Based on a 540watt panels, the house could hold 14 panels totalling 7.5kw array

The garage could hold 2.7kw array

 

I would also like it to work in a power cut.

 

Now, where do I start? My budget would be £15-20k tops for panels and batteries.

Ultimately, I want the biggest array possible when the scaffolding is up hence the 500+ watt panels, and ultimately be as off grid as possible. I would probably want to register for feed in tariff payments, just so that is set up.

 

Looking at our  usage, and (https://re.jrc.ec.europa.eu/pvg_tools/en/) a 7.5kw array could produce 9.3 kwh in December, rising to 31.5kwh in June. So almost cover all of our current electricity use for the majority of the year on average.

If we got a 10kw array (using the garage aswell), that would be 12 kwh in December, rising to 42kwh in June.

 

The surplus, I would look into storing hot water, Elec heating/cooling for the house and a future EV.

I’m not sure if it’s possible to install a hot water tank due to the weight, although do have the space upstairs. So I like the idea of something like SunAmp. But I accept this is the next step after panels and batteries.

 

I also like the idea of topping up on a cheaper night time tariff if required (but may not be required with such a large array).

 

What systems do people recommend? I liked the idea of a Tesla Power Wall, but I don’t think I can have more than one due to needing a 3 phase? Secondly, they are completely unavailable now. I’ve read Solar Edge only works with their own components, so you’re tied to them if you go that route. I don’t have a clue what the best panels or inverter are.

 

What size batteries do you think I would require? Obviously the larger the better, but something like 25 kwh (i.e. 3 days average usage)?

 

I’m aware some people say do it in stages (panels, then batteries), but I would rather it all installed and working in one hit. I would also want to give me as much power as possible during winter when top up from the grid is inevitable.

 

Thanks!

[Marvin]

Hi @jason213

 

This may help with your battery calculations...

 

Based on your home with 10kW system this is December 2020's calculated daily production using the PVGIS. Note the variance over the days:

(assumptions: GU32  10kW, roof angle 40 deg, Azimuth -22, system loss 5%) 

 

24,017
4,442
1,515
4,119
11,816
16,774
3,285
28,062
8,637
1,278
8,262
18,298
1,967
2,024
11,259
2,634
11,027
1,282
11,197
19,542
3,870
5,990
3,988
27,743
28,824
2,816
23,547
2,730
12,745
21,850
15,055

Total for December.   340,593kWh

 

Of course this is just December 2020. Other Decembers can vary widely from year to year.

 

Good luck

 

M

 

[Benguela]

12 hours ago, Jason213 said:

I would probably want to register for feed in tariff payments, just so that is set up.

Feed in tariff is gone.

 

But you can get Smart Export Guarantee.

 

Also, Octopus Outgoing tariff is very good at the moment.

 

I've got a SolarEdge inverter and, it is as you say: if you install SE you are tied to using SE.

 

My advice would be to start your planning around the inverter that you want. Find the right inverter first because that's the brains of your system. Then build everything else around that.

[Dillsue]

43 minutes ago, Benguela said:

I've got a SolarEdge inverter and, it is as you say: if you install SE you are tied to using SE.

Youre only tied to SE if you want DC coupled batteries. AFAIK you can have AC coupled from any supplier

Edited September 22, 2022 by Dillsue

[Marvin]

Put as many panels up as possible is my advice. Knowing that you will be above the permitted export allowance you will have to apply to the DNO (distribution network operator ) for their permission. (DNO Survey: will the local mains cables take the load/supply. will the substation take these changes, will the supply cables to your home take these changes and so on) Last fee I was charged was £300+vat for the SURVEY and about two to 3 month for reply. The survey can state that other works will need to be carried out to achieve your installation. Read the small print on the application about what your agreeing to pay for by submitting the application! The application has to be done BEFORE the installation is commenced. I would suggest before any decisions are made (you buy all the gear and they say the infrastructure changes will cost you £10k for example).

 

Be aware that battery storage before the inverter will not make a difference to your exporting capability. Battery storage after the inverter will, and will need to be added to the amount your are proposing to export (as far as I understand)

 

Calculations for the DNO will be based on the maximum that the Inverter will export (not on the amount of PV on the roof etc) and calculated on 'after Inverter battery supply'. (As above, if I have this right).

 

If you don't do this all at the same time, you will then need to apply for the increase in potential upgrade later. (you could go for just the permitted now but the inverter would be too small in the future....)

 

Check battery for power volume to output. One of my 100amp 12v batteries can only supply about 40% of it's capacity before damaging the battery. So I need 2.5 times the storage of what I want to use. Other battery types will have a higher capacity to supply but will cost more...

 

Depending on the inverter you can install more PV panels than the invert will export. Ours is limited to 6000W but you can install almost 8000W

 

Hope this helps

 

M

Edited September 22, 2022 by Marvin
further thought

[Pocster]

Good advice here .

Initially I had a 4kw pv array and a PowerWall 2 . Really pleased with it . But before war and energy hikes I decided to get the array doubled and wanted more storage ( the aim being to never take from the grid at peak rate ) . As you mention PW wait times are 18 months + . I went for a SolarEdge battery . It’s a bit of a fiddle to get them to play nice - but is doable . 
I would choose your system now battery wise as you’ll be in a long queue anyway . PV as big as you can go . Inverter as large as DNO will allow would be my advice . As getting a battery is someway off I would get an EV sooner rather than later ( though they can be hard to come by ) . Objective being to export as little as possible .

[Benguela]

1 hour ago, Dillsue said:

Youre only tied to SE if you want DC coupled batteries. AFAIK you can have AC coupled from any supplier

True... but if you're going for an AC coupled solution then you need yet another inverter.

 

You'll have your SE inverter to turn your DC solar into AC for use in your house. And then you'll take that house AC and, using another inverter, invert it back to DC to store in your AC coupled battery.

 

So why not just have one inverter from the start? Hence my advice to start with the inverter that you want and to build everything else around that.

[Dillsue]

25 minutes ago, Benguela said:

So why not just have one inverter from the start? Hence my advice to start with the inverter that you want and to build everything else around that.

Op wants power in a power cut and is already talking about a Powerwall which will provide power in a cut but wont process PV, so 2 inverters. Im not sure if theres any UK certified systems that will do backup and process PV?? I think Solaredge already have PB/backup inverter certified for the US but not the UK yet. May be there are other systems??

[Jason213]

Hi Thanks for the replies.

 

@ Marvin. Thanks for the data, so 10kw array would have produced approx just under 11kwh in Dec2020.

So that, with adequate 3 day storage, would cover my current electrical needs.

 

@Benguela. Sorry I meant SEG

 

For an EV, I can't justify the huge price tags at the moment, whereas my car still has lots of life left in it.

 

 

So, in summary I need to decide:

 

Go for a maximum array, with many DC batteries but an inverter limited to the max export rate (3.86 kw? i think).

Downsides: No power outage cover, and won't supply peak power

Upsides: No DNO application, theoretically cheaper,

Conclusion: excess power can still be put into heating/hot water (SunAmp) or cooling if required, and then export at the limited rate. However in the summer months I'm sure lots of energy will be lost (without an EV).

 

Go for AC batteries,

Downsides: A DNO application, higher cost, larger inverter

Upsides: Power outage option, export what I don't need and cant' store.

 

 

I think I need to look at the DNO application, as I prefer the later option (until I find out the cost). So it's the G99 form for SSEN, although this is very confusing to fill out.

 

 

 

[Pocster]

I have 1 inverter for all I.e pv , se , pw 

[Pocster]

1 minute ago, Jason213 said:

Hi Thanks for the replies.

 

@ Marvin. Thanks for the data, so 10kw array would have produced approx just under 11kwh in Dec2020.

So that, with adequate 3 day storage, would cover my current electrical needs.

 

@Benguela. Sorry I meant SEG

 

For an EV, I can't justify the huge price tags at the moment, whereas my car still has lots of life left in it.

 

 

So, in summary I need to decide:

 

Go for a maximum array, with many DC batteries but an inverter limited to the max export rate (3.86 kw? i think).

Downsides: No power outage cover, and won't supply peak power

Upsides: No DNO application, theoretically cheaper,

Conclusion: excess power can still be put into heating/hot water (SunAmp) or cooling if required, and then export at the limited rate. However in the summer months I'm sure lots of energy will be lost (without an EV).

 

Go for AC batteries,

Downsides: A DNO application, higher cost, larger inverter

Upsides: Power outage option, export what I don't need and cant' store.

 

 

I think I need to look at the DNO application, as I prefer the later option (until I find out the cost). So it's the G99 form for SSEN, although this is very confusing to fill out.

 

 

 

I’m not sure about your “ can’t meet demand “ quote . If my SE is set correctly and PW goes over it’s 5kw limit SE and/or PV take up the slack . So my maximum “load” is 5k (pw ) + SE (3.68k) . So I would assume multiple SE or PW ( other makes ) can provide greater loads combined ???? 

[Dillsue]

1 hour ago, pocster said:

I have 1 inverter for all I.e pv , se , pw 

Theres a DC-AC inverter in the powerwall on top of the SE PV one!

[Pocster]

1 minute ago, Dillsue said:

Theres a DC-AC inverter in the powerwall on top of the SE PV one!

I know . It didn’t want to give the impression you need a 2nd I.e external inverter ( so 3 in total ! 😁 ) 

[Dillsue]

1 hour ago, Jason213 said:

I think I need to look at the DNO application, as I prefer the later option (until I find out the cost). So it's the G99 form for SSEN, although this is very confusing to fill out.

Speak to them first as you may get an indication of likley export limits without making a formal application. SPEN did an informal assessment on our limit and we had an agreement in a few days. Sent the formal G99 application in to reflect what we'd already agreed so straight forward approval. Not sure all DNOs are that slick though!!

[Dillsue]

4 minutes ago, pocster said:

I know . It didn’t want to give the impression you need a 2nd I.e external inverter ( so 3 in total ! 😁 ) 

It was the integral PW one that triggered the 2 inverter discussion earlier!